docs: def _timestamp_zero_start_handler(c, ctx):
      """Handles numeric values that start with a zero followed by another digit. This is either a timestamp or an
      error.
      """
      val = ctx.value
      ctx.set_ion_type(IonType.TIMESTAMP)
      if val[0] == _MINUS:
          _illegal_character(c, ctx, 'Negative year not allowed.')
      val.append(c)
      c, self = yield
      trans = ctx.immediate_transition(self)
      while True:
          if c in _TIMESTAMP_YEAR_DELIMITERS:
              trans = ctx.immediate_transition(_timestamp_handler(c, ctx))
          elif c in _DIGITS:
              val.append(c)
          else:
              _illegal_character(c, ctx)
          c, _ = yield trans